Recently, Tangs et al. have manufactured an organic electroluminescent device (hereinafter sometimes referred to as an “organic EL device”) having a two-layer structure, which consists of a luminescent layer formed of an organic fluorescent dye and a layer formed of an organic charge-transport compound, for example, used in an electrophotographic photoreceptor (Patent Document 1, JP-A-59-194393). There is another report that when a small amount of fluorescent dye is doped to an electron-transport luminescent layer, the fluorescent dye emits light, with the result that a long-life device with high-efficiency can be obtained. An organic EL device is driven by low voltage application and has high brightness compared to competitive devices. In addition to these characteristics, multiple-color emission can be easily obtained. Therefore, many studies have been conducted on the structure of the device, organic fluorescent dyes and organic charge-transport compounds to be used in the device and reported in Non-Patent Document 1: Jpn. J. Appl. Phys. Vol. 27, Page L269 (1988); and Non-Patent Document 2: J. Appl. Phys. Vol. 65, Page 3610 (1989).
Furthermore, separately from organic EL devices primarily using a low molecular-weight organic compound, polymer luminescent devices using a polymer luminescent material (hereinafter referred to as a “polymer fluorescent”) have been proposed, for example, in Patent Document 2 (WO9013148 pamphlet); Patent Document 3 (JP-A-3-244630) and Non-Patent Document 3 (Appl. Phys. Lett. Vol. 58, Page 1982 (1991)). The pamphlet of WO9013148 discloses, in an Example, a device using a thin film of poly(p-phenylenevinylene) (hereinafter sometimes referred to as “PPV”), which is a conjugated polymer formed by applying a soluble precursor onto an electrode to form a film, and subjecting the film to heat treatment (thereby converting to the conjugated polymer).
Such a conventional organic EL device has been improved in material and device constitution. As a result, the brightness and life thereof have been enhanced but do not reach practical levels required for use in display and illumination.
Such a conventional organic EL device has a single luminescent unit containing a luminescent layer between electrodes facing each other. To improve the performance thereof, an organic EL device (sometimes called a stacked device), which has a plurality of luminescent units containing a luminescent layer and individually partitioned by a charge generating layer between the electrodes facing each other, has been proposed (Patent Document 4: JP-A-2003-272860)
Patent Document 1: JP-A-59-194393
Patent Document 2: WO9013148 pamphlet
Patent Document 3: JP-A-3-244630
Patent Document 4: JP-A-2003-272860
Non Patent Document 1: Jpn. J. Appl. Phys. Vol. 27, Page L269 (1988)
Non-Patent Document 2: J. Appl. Phys. Vol. 65, Page 3610 (1989)
Non-Patent Document 3: Appl. Phys. Lett. Vol. 58, Page 1982 (1991)